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The first computer mouse was invented in the early 1960's by Douglas Engelbart during his time at the Stanford Research Institute in Menlo Park, California. Engelbart was described as a visionary during the 1950s and '60s when a single computer enveloped an entire room.
Early prototypes of the mouse consisted of a rectangular wooden shell with two metal balls inside: one for the X axis and one for the Y axis. It only had one button on the corner. The device was originally designed to work with the Xerox Alto computer system and was referred to as the "X-Y Position Indicator for a Display System." Later on Engelbart himself would coin the term "mouse."
As you can imagine, a device of this nature was well ahead of its time but perhaps nobody ultimately realized that more than Engelbart himself. The mouse didn't become commercially viable until Apple's Macintosh hit the scene in 1984. By 1987, however, the patent on his device expired and landed in the public domain.
This meant that Engelbart and his colleagues weren't able to collect royalties on the mouse once it became widely used. Well over a billion mice have been sold since the mid 1980s.